1. Field of the Invention
The present invention relates to an image forming apparatus including a scanning optical system which, using a plurality of beams issued from a plurality of optical fibers, records and forms electrostatic latent images on a photosensitive member.
2. Description of the Related Art
In the field of an image forming apparatus such as a printer or copying machine, year after year, there has increased a demand that a high-precision image can be printed at a high speed. To meet this demand, in a so called laser printer, there is proposed and practically used a beam scanning apparatus in which the number of beams to scan a photosensitive member at the same time is increased and scanning is executed using two beams in a lump to form an electrostatic latent image on the photosensitive member, thereby being able to enhance the image printing speed.
However, although the above-mentioned two-beam scanning apparatus is suitable for use in a middle-speed printer which prints several dozens of pages per minute, the two-beam scanning apparatus is not effective for use fin a superhigh-speed printer which prints hundreds of pages per minute. Thus, in such superhigh-speed printer, there has been practically used a scanning apparatus using three or more beams.
Now, FIG. 7 shows an example of an image forming apparatus including a scanning apparatus using three or more beams. In this example, there is shown an image forming apparatus which uses five beams.
In FIG. 7, reference character 1 designates an optical fiber. On the one-end portions of five optical fibers, there are mounted semiconductor laser modules 28 respectively. Here, in each of the semiconductor laser modules 28, there are incorporated not only a semiconductor laser (not shown) serving as a light source but also, for example, as disclosed in JP-A-8-222806 and JP-A-9-113832, one or more lenses.
The other-end sides (that is, the sides on which the semiconductor laser modules 28 are not mounted) of the respective optical fibers are held in a lined-up manner and form an optical fiber arrangement portion 29.
Five beams, which have been emitted from the optical fiber arrangement portion 29, enter a deflector (rotary multi-surface mirror) 23 through lenses 24, 25, 26 and 27 which are respectively disposed on an optical path. The five beams, which have been reflected by the rotary multi-surface mirror 23, pass through an image forming lens 22 and scan the surface of a photosensitive member 21 collectively.
The optical fiber arrangement portion 29, as shown in FIG. 9, is composed of an optical fiber 1, a silicone base plate 31, and a glass plate 33. The optical fiber 1 is composed of a clad 13 having a outside diameter of 125 xcexcm, and a core 12 which is used to transmit the beams and has an outside diameter of 4 xcexcm. In the silicone base plate 31, there are formed V grooves 32 which are formed at intervals of 150 xcexcm by the anisotropic etching of silicone crystal so that they can be used to arrange the respective optical fibers 1 in a lined-up manner. Specifically, the optical fibers 1 are put in the V grooves 32 one for one, the optical fibers 1 are respectively held by the glass plate 33, gaps formed between the silicone base plate 31 and glass plate 33 are filled with ultraviolet hardened resin 14, and the silicone base plate 31 and glass plate 33 are bonded together, thereby producing the optical fiber arrangement portion 29.
By the way, in this type of scanning apparatus using a plurality of optical fibers, the optical fiber arrangement precision is extremely important. That is, in case where the five optical fibers are arranged in a line at equal intervals, as shown in FIG. 8A, there can be obtained, on the photosensitive member, scanning lines which are disposed at equal intervals. However, in case where the arrangement precision of the optical fibers is low, as shown in FIG. 8B, the intervals between the scanning lines vary, which, of course, has ill influences on an image that is formed on the photosensitive member; that is, the quality of the image is impaired, for example, there is caused shear in the image.
The present invention aims at eliminating the above drawbacks found in the conventional image forming apparatus. Accordingly, it is an object of the invention to provide an optical fiber arrangement portion in which a plurality of optical fibers are arranged with high precision and thus realize an image forming apparatus which is capable of high quality image printing.
In attaining the above object, according to the invention, there is provided an image forming apparatus, comprising: a plurality of semiconductor laser modules each mounted on one end portion of an optical fiber for emitting a beam issued by a semiconductor laser toward the other end side of the optical fiber; an optical fiber arrangement portion for arranging therein the beam emitting ends of optical fibers respectively mounted on the semiconductor laser modules; and, a scanning optical system for recording and forming electrostatic latent images on a photosensitive member using a plurality of beams emitted from the optical fiber arrangement portion,
wherein each of the optical fibers includes on the outer peripheral portion thereof a plate member to be used when assembling the optical fiber arrangement portion, and the optical fiber arrangement portion includes an optical fiber arrangement in which the plate members of the optical fibers are superimposed on top of each other in parallel to each other.